Dennis,
R.E. Lee probably owned a number of different sidearms purchased by him or presented to him during his years of service in the U.S and C.S. Army.
I do know that the Museum of the Confederacy in Richmond, VA, has on display his Colt Model 1851 Navy revolver, or at least had it on display with a number of his other personal possessions the last time I visited the museum.
Mike